1. Field of the Invention
The present invention relates to a distance measuring device, an image forming apparatus, and a distance measuring method.
2. Description of the Related Art
A typical inkjet image forming apparatus ejects ink from a recording head while moving a carriage, on which the recording head is mounted, in a reciprocating manner in a main-scanning direction, and forms an image on a recording medium. In this system, even if it is intended to attach the ink to the same position on the recording medium in forward movement and backward movement of the carriage, a positional deviation may occur. The positional deviation as described above may be referred to as a deviation of an ink landing position.
The deviation of the ink landing position may occur due to not only a difference in moving directions in the reciprocating movement but also an assembly error of the recording head with respect to the carriage, for example. That is, when an image is formed by using a plurality of recording heads, a relative positional relationship among the recording heads may not be maintained as designed due to an assembly error of each of the recording heads with respect to a carriage, and a deviation of an ink landing position among the recording heads may occur.
If the deviation of the ink landing position occurs, it is necessary to resolve the positional deviation by, for example, adjusting a parameter related to a position at which an image is formed by an image forming apparatus. To adjust the image forming position as described above, a method has been proposed in which a predetermined test pattern is formed on a recording medium, various sensors read the test pattern, and a deviation of an ink landing position is detected. For example, Japanese Patent Laid-open Publication No. 2011-161718 describes a method, in which a test pattern is formed so as to include a first dot group that is formed during forward movement of a carriage and include a second dot group and a third dot group that are formed during backward movement of the carriage, a two-dimensional image sensor captures an image of the test pattern, two-dimensional frequency characteristics of the test pattern is acquired by analyzing the captured image, and a deviation of an ink landing position between the forward movement and the backward movement of the carriage is detected based on the two-dimensional frequency characteristics.
To appropriately adjust the image forming position in accordance with the deviation of the ink landing position, it is necessary to obtain an amount of the positional deviation. As in the method described in Japanese Patent Laid-open Publication No. 2011-161718, when a method of detecting the deviation of the ink landing position by analyzing the captured image of the test pattern captured by the two-dimensional image sensor is to be used, it is possible to appropriately adjust the image forming position in accordance with the deviation of the ink landing position if an amount of an actual positional deviation (actual distance) can be obtained from the amount of the positional deviation in the captured image corresponding to the detected deviation of the landing position.
However, in the method described in Japanese Patent Laid-open Publication No. 2011-161718, while it is possible to detect an occurrence of the deviation of the ink landing position by analyzing the captured image of the test pattern, it is difficult to detect the amount of the positional deviation. Furthermore, even if the amount of the positional deviation in the captured image can be obtained, it is necessary to obtain a ratio of a distance in the captured image and an actual distance in order to obtain an actual distance from the amount of the positional deviation in the captured image. However, the ratio of the distance in the captured image and the actual distance changes with a change in a distance between the two-dimensional image sensor and an object, so that in an environment in which the distance between the two-dimensional image sensor and a detection pattern changes, it is difficult to obtain the actual distance from the amount of the positional deviation in the captured image.